Evolution and regulation of the Z chromosome

Males and females of many species differ in morphology, physiology, and behavior. In taxa with genetic sex determination, sexual differentiation arises largely from sex-biased gene expression, which varies across tissues, developmental stages, and lineages. Increasing evidence highlights chromatin configuration, which can exist in open or closed states, and can be shaped by sex-determination path ways, as a key regulatory layer of this dimorphism. Degeneration of the Y or W chromosome further contributes to sex -specific differences by altering gene copy numbers relative to autosomes in heterogametic sex. To mitigate these imbalances, many eukaryotes have independently evolved dosage compensation mechanisms, often mediated through chromatin -level regulation. In this thesis, we investigate the evolutionary dynamics of sex chromosome differentiation in two species, Artemia franciscana and Cameraria ohridella , with a particular focus on the extent of dosage compensation following gene loss in the heterogametic sex and the potential chromatin-based mechanisms underlying this process. We further characterize sex -biased gene expression and its regulation through histone modifications. Our analyses also reveal that the A. franciscana genome is highly repetitive, with many genes containing intronic transposable elements. We find that enrichment of histonemo difications associated with constitutive heterochromatin, positively correlates with variation in gene expression levels. Collectively, these findings underscore role of chromatin regulation in shaping the evolution of sex chromosomes and sexual differentiation.